1. Field of the Invention
The present invention is generally related to an exhaust elbow for a marine propulsion system and, more particularly, to an exhaust elbow that provides a water collection cavity for the purpose of preventing the flow of water, in a reverse direction, through the wet exhaust system of a marine propulsion engine.
2. Description of the Prior Art
Many different types of exhaust systems for marine propulsion engines are well known to those skilled in the art. Some of these exhaust systems incorporate an exhaust elbow which serves as a transition from the exhaust manifold of an internal combustion engine to an exhaust pipe assembly of a marine vessel.
U.S. Pat. No. 4,573,318 which issued to Entringer et al on Mar. 4, 1986, discloses an exhaust elbow for a marine propulsion system which has an intake exhaust passage extending upwardly from the engine and communicating through a bend with a discharge exhaust passage, and a water jacket having pockets around the exhaust passages for cooling the latter. A central channel extends longitudinally along the exterior of the exhaust passages to guide water therealong to the end of the discharge exhaust passage to mix with exhaust gases. The central channel has a pair of sidewalls extending longitudinally and laterally tapered away from each other at the outer end of the discharge exhaust passage to create an outward draw from the central passage to minimize break-up of longitudinally outward water flow and maintain the end tip of the discharge exhaust passage dry and prevent water ingestion and creeping back into the discharge exhaust passage due to pulsations of the engine. Dam and port structure is also provided enabling faster heating of the exhaust passage and, in turn, minimize the condensation within the elbow which may otherwise ingest back into the engine.
U.S. Pat. No. 4,845,945, which issued to Widmer et al on Jul. 11, 1989 discloses an exhaust elbow trough. A water jacketed exhaust elbow for a marine propulsion system includes an intake exhaust passage communicating with a discharge exhaust passage, a water jacket around the exhaust passages, and a trough member extending longitudinally along a water channel along the exterior of the discharge exhaust passage to guide water therealong to mix with exhaust at the end of the discharge exhaust passage. The trough member extends beyond the end tip of the discharge exhaust passage and has a sharp edge providing a clean parting surface for the coolant water and preventing ingestion of water back into the discharge exhaust passage.
U.S. Pat. No. 5,109,668, which issued to Lindstedt on May 5, 1992, discloses a marine exhaust manifold and elbow. The exhaust assembly includes a manifold portion, an elbow portion, a water jacket portion, and exhaust runner walls, providing a smooth continuous transition of exhaust gas flow from intake exhaust passages in the manifold portion to transfer exhaust passages in the elbow portion around a bend to a discharge exhaust portion, minimizing turbulent flow of exhaust through the manifold portion and elbow portion. Each transfer exhaust passage has its own water supply inlet at the upstream end of the respective intake exhaust passage. An upper vent includes a steam outlet opening in the water jacket at the high point of the elbow portion, and a steam exhaust channel extending along the top exterior of the water jacket portion in a raised bead above and parallel to an upper water flow passage and directing steam to the end of the discharge exhaust passage to mix with water and exhaust thereat. Wall supports assist in directing cooling water up through the water jacket to the top of the elbow bend, and also prevent wall collapse during lost foam stainless steel casting processes.
U.S. Pat. No. 6,022,254, which issued to Neisen on Feb. 8, 2000, describes an exhaust system for inboard/outboard marine propulsion systems. The exhaust system includes intermediate exhaust pipes which are physically separate components than the water separator. A sealed latching mechanism connects an outlet portion of the intermediate exhaust pipes to an inlet portion of the water separator. The sealed latching mechanism is secure yet flexible and allows the orientation of the intermediate exhaust pipe to be adjusted relative to the water separator, thus allowing the exhaust system to be installed and serviced without dismounting or loosening the engine. The intermediate exhaust pipes also have a flared inlet port to facilitate a alignment of the intermediate exhaust pipe at the exhaust elbow.
U.S. Pat. No. 5,644,914, which issued to Deavers et al on Jul. 8, 1997, discloses an exhaust pressure pulsation control apparatus for a marine propulsion system. The apparatus has a front ring and a reflector disk located downstream of the front ring. There is a space between the front ring and the reflector disk that is sufficiently large so that the mixture of water and water cooled exhaust passing through the apparatus does not have a significant pressure drop.
The apparatus attenuates pressure pulsations in the exhaust system, thereby significantly reducing water ingestion through the exhaust system into the engine.
The apparatus does not create significant exhaust back pressure, and typically increases engine maximum power output.
U.S. Pat. No. 4,734,071, which issued to Zemlicka et al on Mar. 29, 1988, discloses a marine engine exhaust assembly. The assembly is provided with water flow path control devices which minimize back pressure. Lower intermediate elbow portions and the respective bullhorn upper legs are formed and joined in a manner to provide a continuous common gas-water passage which is axially linear in a fore-to-aft direction. The common gas-water passages are formed to provide a gradual reduction in cross-sectional area from top to bottom. The wall contours of the intermediate elbows gradually merge from circular at the upper end to generally elliptical at the lower end. In addition, the wall contours of the upper bullhorn legs are generally elliptical at their upper ends for communicating with the intermediate elbows, and gradually merge into a rectangular shape in the area of the bullhorn bends, which continues on to adjacent the bullhorn discharge portion. The leading edges of the gas-water separator plates are formed with a generally V-shaped downstream curve which provides a slicing edge for the water. A gimbal housing has water-carrying lightening pockets which connect from the bullhorn to drain holes in the housing body. The lightening pockets are short and terminate adjacent their respective drain holes. The inner pocket ends are broadly curved in the direction of the respective drain holes.
U.S. Pat. No. 3,759,041, which issued to North et al on Sep. 18, 1973, describes an exhaust water separator for marine engines. Exhaust elbows are provided which force cooling water in the exhaust to the outside by centrifugal action. This water is removed and expelled through the transom.
The patents described above are hereby explicitly incorporated by reference in the description of the present invention.
Modern high output engines of marine propulsion systems require low restriction exhaust systems in order to obtain the maximum horsepower potential from the engines. Unfortunately, exhaust systems for marine propulsion systems known to those skilled in the art typically achieve low restriction exhaust systems with designs that result in low exhaust flow velocities when the engine is operated at reduced speeds. This low exhaust flow velocity increases the susceptibility of the engine to draw cooling water back into the cylinders of the engine. Cooling water is discharged into the exhaust systems in many types of known marine propulsion devices and this discharged water can be pulled back from the exhaust conduits and into the cylinders of the engine, causing severe damage. This phenomenon is referred to as "water reversion" and the characteristic is caused by the high valve overlap used on modem engines as well as other factors. Valve overlap is a term that refers to having both the intake and exhaust valve on each cylinder opened simultaneously for a brief period of time for the purpose of allowing the engine to take on more fuel and air at higher engine speeds. While this valve overlap is advantageous for producing more power at higher speeds, it allows intake manifold vacuum to cross over into the exhaust system at idle and low speeds and can result in water being drawn backward within the exhaust system and into the cylinders of the engine. The lower exhaust flow velocities, which typically occur at reduced engine speeds in modern exhaust systems, makes it easier for the exhaust and water to reverse direction and be drawn back into the engine. The problem of water reversion typically occurs at idle and low engine speeds and can be very harmful to the engine.
It would therefore be significantly advantageous if an exhaust system could be provided for a marine propulsion system in which a low restriction exhaust passage could be provided without the disadvantageous characteristics described above.